Field of the Disclosure
The present disclosure relates to a blower that transports gas.
Description of the Related Art    Patent Document 1: Japanese Patent No. 4795428
There have hitherto been known various types of blowers that transport gas. For example, Patent Document 1 discloses a piezoelectrically driven pump.
FIG. 11 is a cross-sectional view of a pump 900 according to Patent Document 1.
This pump 900 includes a piezoelectric disk 920, a disc 912 to which the piezoelectric disk 920 is joined, and a main body 913 that defines a hollow 911 with the disc 912. The main body 913 has an inlet 915 through which gas flows in and an outlet 914 through which gas flows out. The main body 913 has a bottom plate 918.
The inlet 915 is provided in the bottom plate 918 between a center axis of the hollow 911 and an outer periphery of the hollow 911. The outlet 914 is provided in the bottom plate 918 at the center axis of the hollow 911. At the outlet 914, a valve 916 is provided to prevent gas from flowing from the outside to the inside of the hollow 911.
When the pump 900 of Patent Document 1 is operated at a resonant frequency of a third-order mode, the piezoelectric disk 920 bends and vibrates the disc 912. In response to the bending vibration of the disc 912, the bottom plate 918 also bends and vibrates, as illustrated in FIG. 12B. Thus, gas flows from the inlet 915 into the hollow 911, and gas in the hollow 911 is discharged from the outlet 914.
As a result, as illustrated in FIG. 12A, the pressure at each point in the hollow 911 is changed by the bending vibrations of the disc 912 and the bottom plate 918 from the center axis of the hollow 911 toward the outer periphery of the hollow 911.
However, the present inventor found the following problems by superimposing the displacement of each point of the bottom plate 918 shown in FIG. 12B on the pressure change at each point in the blower chamber shown in FIG. 12A in the pump 900 of Patent Document 1 (see FIG. 13).
First, when the pressure of air becomes a positive pressure higher than an atmospheric pressure P1 in a first outer peripheral space Q1 of the hollow 911, as illustrated in FIG. 13, an outer peripheral region of the bottom plate 918 is located apart from an initial position P2 of the bottom plate 918 on a side opposite from the disc 912. That is, when the pressure of air becomes a positive pressure in the first outer peripheral space Q1 of the hollow 911, the outer peripheral region of the bottom plate 918 attempts to decrease the pressure in the hollow 911.
Next, when the pressure of air becomes a negative pressure lower than the atmospheric pressure P1 in a second outer peripheral space Q2 of the hollow 911, as illustrated in FIG. 13, the outer peripheral region of the bottom plate 918 is closer to the disc 912 than the initial position P2 of the bottom plate 918. That is, when the pressure of air becomes a negative pressure in the second outer peripheral space Q2 of the hollow 911, the outer peripheral region of the bottom plate 918 attempts to increase the pressure in the hollow 911.
Therefore, in Patent Document 1, when the pump 900 operates at the resonant frequency of the third-order mode, the pressure resonance of air in the hollow 911 (blower chamber) is reduced by the bending vibration of the outer peripheral region of the bottom plate 918 (vibrating body), and this reduces the discharge pressure and the discharge flow rate.
An object of the present disclosure is to provide a blower that can prevent the discharge pressure and the discharge flow rate from being reduced by the bending vibration of an outer peripheral region of a vibrating body.
To achieve the above object, a blower according to the present disclosure is configured as follows.
The present disclosure provides a blower including:                an actuator including a vibrating body having a first principal surface and a second principal surface and a driving body provided on at least one of the first principal surface and the second principal surface of the vibrating body to bend and vibrate the vibrating body in a vibration mode of a third or more odd order that forms a plurality of vibration nodes;        a housing joined to the vibrating body to form a blower chamber with the actuator and having a vent that allows an inside and an outside of the blower chamber to communicate with each other; and        a restraining plate,        wherein the vibrating body includes an outer peripheral region in contact with an area from an outermost pressure vibration node in the blower chamber, among the pressure vibration nodes formed by the bending vibration of the vibrating body, to an outer periphery of the blower chamber, and a center region located in an inner side portion of the outer peripheral region, and        wherein the restraining plate restrains the outer peripheral region.        
In this structure, the pressure at each point in the blower chamber from the center axis of the blower chamber toward the outer periphery of the blower chamber is changed by the bending vibration of the vibrating body. The blower chamber includes an outer peripheral space in contact with the outer peripheral region of the vibrating body and a center space provided in an inner side portion of the outer peripheral space to be in contact with the center region of the vibrating body.
The blower having this structure operates at a resonant frequency of an odd order vibration mode. While the blower having this structure is operating, when the pressure of gas (for example, air) falls below a reference pressure (for example, atmospheric pressure) in the outer peripheral space of the blower chamber, the bending vibration of the outer peripheral region is suppressed and reduced. When the pressure of gas exceeds the reference pressure in the outer peripheral space of the blower chamber, the bending vibration of the outer peripheral region is suppressed and reduced.
That is, in this structure, the outer peripheral region of the vibration body does not adversely affect the pressure in the blower chamber and does not reduce the pressure resonance of gas in the blower chamber.
Therefore, the blower of the present disclosure can prevent the discharge pressure and the discharge flow rate from being reduced by the bending vibration of the outer peripheral region of the vibrating body. For this reason, the blower of the present disclosure can achieve a high discharge pressure and a high discharge flow rate.
A rigidity of the outer peripheral region is preferably higher than a rigidity of the center region.
With this structure, the restraining member can restrain the bending vibration of the outer peripheral region.
A thickness of the outer peripheral region is preferably larger than a thickness of the center region.
This structure makes the rigidity of the outer peripheral region higher than the rigidity of the center region.
A shortest distance a from a center axis of the blower chamber to an end of an area in an inner side portion of a joint portion of the vibrating body to the housing and a vibration frequency f of the actuator preferably satisfy a relation that af=(k0c)/(2π) wherein c represents an acoustic velocity of gas passing through the blower chamber and k0 represents a value to satisfy a relation that a Bessel function of a first kind J0′(k0) is equal to 0.
In this structure, the vibrating body and the housing are provided to obtain the shortest distance a. The driving body vibrates the actuator at the vibration frequency f.
The value k0 satisfies the relation that J0′(k0)=0 when J0′(k0) is a differential value of the Bessel function of the first kind. Further, the value a represents the shortest distance from the center axis of the blower chamber to the end of the area in the inner side portion of the joint portion of the vibrating body to the housing.
Here, when af=(k0c)/(2π), the outermost node among the vibration nodes of the vibrating body coincides with a pressure vibration node in the blower chamber, and this produces the pressure resonance.
For this reason, when the relation that af=(k0c)/(2π) is satisfied, the blower having this structure can achieve a high discharge pressure and a high flow rate.
The driving body is preferably a piezoelectric body.
The blower having this structure can achieve noise reduction by using, as a driving source, the piezoelectric body that generates little sound and vibration during driving.
A valve is preferably provided at the vent to prevent gas from flowing from the outside to the inside of the blower chamber.
In the blower having this structure, the valve can prevent gas from flowing from the outside of the blower chamber to the inside of the blower chamber through the vent. For this reason, the blower having this structure can achieve a high discharge pressure and a high flow rate.
According to the present disclosure, it is possible to prevent the discharge pressure and the discharge flow rate from being reduced by the bending vibration of the outer peripheral region of the vibrating body.